1. Field of the Invention
This invention relates to hydrophobic lignocellulosic materials and a process for producing them, as well as composite materials containing them. The hydrophobic lignocellulosic materials have wide application in products requiring high dimensional stability and excellent adhesion as in fibre-based packaging, decorative laminates, furniture and non-structural biocomposites.
2. Description of the Prior Art
Lignocellulosic fibres are hydrophilic. This renders them highly susceptible to loss of mechanical properties upon moisture absorption, which is a critical shortcoming for paper and board applications requiring a high degree of dimensional stability and low hygroexpansivity. In addition, the highly polar nature of lignocellulosics makes them poorly compatible with commonly non-polar polymers used in the production of textiles and composites. One possible solution to this limitation could be the enhancement of the surface energy of lignocellulosic materials. Surface modification has been used to target several applications of modified cellulosic materials such as: cellulose ion exchangers, antibacterial papers, protein immobilizers, composite material, products for mercury (II) removal from wastewater. Surface modification can potentially enhance the compatibility of lignocellulosic fibres with polymers in composites and related applications.
All reported applications for developing moisture-resistant paper and board products involve the application of hydrophobic surface coatings to the finished product. For example, U.S. Pat. No. 6,846,573 to Seydel, discloses the preparation of moisture resistant and water proof paper products that can be repulped and recycled, through use of hydrogenated triglycerides as surface coatings.
Other methods have been reported to prepare hydrophobic fibres. For instance, U.S. Patent Application No. 2005/0245159 A1 to Chmielewski discloses a technique to prepare breathable barrier composites with hydrophobic cellulosic fibres by applying a polymeric sizing agent such as alkyl ketene dimer. Although this chemical is purported to be covalently attached to the surface of the fibres, the modified fibres are only moderately hydrophobic.
U.S. Pat. No. 3,770,575 to Ball discloses a method for making a hydrophobic fibrous product that may be used to absorb oil from the surface of water. The hydrophobic fibres are made from a synthetic sizing agent, and the sized pulp is then dried and compressed in bales. This technique was employed by Bergquist, U.S. Pat. No. 5,817,079, in which Bergquist discloses a selective placement of absorbent product materials in sanitary napkins and the like. U.S. Pat. No. 4,343,680 to Field discloses a method for the preparation of hydrophobic oleophilic wood pulp by treating high yield wood pulp at high temperature for about 16 hours followed by fluffing of the heat treated pulp. According to the inventors, this hydrophobic pulp may be used as an inexpensive absorbent for oil spills and the like.